The Seagrass Filefish, Acreichthys tomentosus (Linnaeus), a master of camouflage

The filefishes of the family Monacanthidae are well known for the ability of many of the species to avoid detection by changing their color pattern to that of the immediate environment. Some enhance the deception by adding nodules, filaments, or flaps to the skin, and by their behavior. The Seagrass Filefish, Acreichthys tomentosus (Linnaeus), effectively uses all of these guises. The research site is the Marine Reserve Park of the Davao del Norte State College in the northern Davao Gulf, Mindanao, Philippines. Juveniles of the filefish are usually found remarkably well hidden in benthic algae of several species. Subadults and adults are most often seen in seagrass beds (in the reserve mainly tape grass, Enhalus acoroides), where they match the color of the amount of epiphytic growth on the seagrass. They feed mainly on the epiphytes of the seagrass. The seagrass and the filefish are an example of symbiosis (ecologists prefer mutualism). Unchecked, the accumulation of epiphytic growth will kill the blade of sea grass. The filefish not only changes its color pattern to match that of a new environment, but is able to instantly alter the texture of its skin, including producing filaments a few mm in length. A plan to videotape the change in the skin in an aquarium, followed by histological study of the filefish skin was cancelled when we learned that Allen et al. (2006) published the same remarkable sequence with the filefish Monacanthus tuckeri in the Caribbean Sea. Acreichthys tomentosus occurs throughout the Indo-Malayan region, ranging north to the Yaeyama Islands of Japan, south to Queensland, east to Tonga, and west to Sri Lanka; an East African record is a probable error.